Transmitter



Patented Mar. 19, 1929.

UNITED STATES 1,706,191 PATENT' OFFICE.

ARTHUR BESSEY SMITH, F EVANSTON, ILLINOIS, ASSIGNOB- TO RESERVE HOLDING COMPANY, OF KANSAS CITY, MISSOURI, A CCRPORATION OF DELAWARE.

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Application filed August 11, 1927. Serial No. 212,176.

This invention relates to telephone transmitters of the carbon granule type, and the principal object is to provide a microphoneelement structure in this type of transmitter which will more effectively distribute the granular carbon in the microphone cell and.

applied by the vibrating diaphragm. In acertain area between the piston or pusher and the fixed electrode, a comparatively thin and restricted region is formed, across which the current must pass to flow through the granules. The carbon in this thin restricted region of current flow will be at its maximum activity when the diaphragm is vibrated, while the space around it Wlll. contain a reserve supply of carbon granules which enables the restricted region to be always filled with carbon, regardless of what position the transmitter is held in. It will therefore never become open circuited. A greater unit per area of pressure of the piston consequently produces greater resistance varlatlons 1n the carbon granules and the range of transmission is correspondingly increased because the mitters of this type.

increased amplitude of current variations, produces clearer and more distinct articulation than has been known before in trans- The packing of the carbon granules and the consequent lowcurrent losses caused thereby, are entirely obviated by the construction of the electrodes, and by the fact that the current can only flow through a region where tlie greatest agitation of the. granules takes p ace.

The foregoing and other useful objects are attained through means which will be fully described hereinafter, reference being had to the accompanying drawing in which Fig. 1 is'a sectional elevation of a transmitter embodying the invention; and Figs. 2 and 3' sectional views of modifications of the microphone elements shown in Fig. 1.

Except for the microphone element, the transmitter ma be of any well known design, As illustrated in the drawing, Fig. 1, it com prises a mouth piece 1; face plate 2, having an opening into which the mouthpiece is screwed; a heavy flanged ring 3 screwed into a threaded flange on the rear of the face plate; a bridge 7 formed integrally with the ring 3; and a microphone cell supported in the center of the bridge 7. A flat ring 6 of insulating material on the back side of the face plate 2 forms a rest for the main diaphragm 5 which receives the speech vibrations. i

The microphone consists essentially of the cup 9, which forms one electrode; the rear electrode 16, the piston 15, the granular mass of carbon around and between the electrodes, and the coupling arrangement between the pusher or piston 15, and the mica auxiliary diaphragm 17 and the main diaphragm 5.

The cup shaped electrode 9 is constructed of brass and its opening is closed by the auxiliary diaphragm 17. This diaphragm may be either conducting or non-conducting, preferably the latter. It is held against the edge of the cup 9 by the brass clamping ring 8 which has a threaded flange that engages the exterior threaded part of the cup 9. An

insulating ring or washer 14 is also clamped between the diaphragm and clamping ring 8 so as to absorb any irregularities in the diaphragm. The round piston 15, having a threaded extended shank, is held in the center of the diaphragm 17 by the clamping disk 13 and a nut 10 threaded on the extended shank of the piston. The surface 27 of this pistonjn the microphone chamber, is suitaly coated with insulating material such as lacquer or enamel to insulate it from the carbon granules so that no current can flow through it. clamped between two nuts 11 and 12 on the shank of the piston 15, so that this diaphragm and the auxiliary diaphragm 17 will vibrate in unison when in use.

The round rear electrode 16 lies in the bottom of the cup 9 and is insulated therefrom by the insulating washer 20. A shank of this electrode extends through a hole in the cup 9 and is insulated from it andthe bridge piece 7 by the insulating bushing 26. Part of the face of this electrode is dished out. while the other part and its circumference are covered by a suitable insulating material 18, so that the carbon granules can only come in contact with the electrode 16 at the dished out portion of its face. Spaced on the bush- The main diaphragm 5" is 1 ing 26 between the bridge piece 7 and the cup 9, is the terminalplate 21 lying against .the cup 9, and the insulating strip 22 which in turn lies against the bridge 7. This terminal plate 21 serves to carry current to the cup shaped electrode 9, while an additional terminal plate 24, insulated from the bridge piece 7 by the insulating washer 23 carries current to the shanlr ofthe electrode 16. A nut 25 screwed onto the shank of the electrode 16 secures the Whole microphone assembly onto the bridge piece 7 as a unit.

When thistransmitter is in operation the current flow takes place over the following path: from the wire attached to the terminal plate 21 to the brass electrode 9, then from the inside surface of the cup of the electrode 9 through the carbon granules and the re ion 19 where the maximum activity of the caroon mass takes place; then to the dish shaped surface of the electrode 16, through the shanlr of this electrode to the terminal plate 24 to which the wire is attached. All current flow takes place over this path and it will he noted that, as the main diaphragm and the auxiliary diaphragm 1'3 together with the piston are vibrated, the fiat circular region indicated at 19, through which all the current must flow, has pressure exerted on it bythe piston 15, a great deal more than the region surrounding the cup electrode 9 and inside the dish shaped region of the electrode 16. While the carbon granules in these-latter regions are agitated to some extent by the piston 15 and the dia phragm 17, they constitute a more or less high constant resistance path for the current to flow through, the greatest resistance variation taking place at the region 19 through which all the current must flow.

l/Vith this type of construction of the microi phone cell it will be seen that regardless of the position of the transmitter when in use, the current fiow cannot be-interrupted through the cell because the region outside the region 19 will always adjust itself so that there will be carbon granules at this place 19.

In the modification shown in Fig. 2, the ele- .ments of themicrophone are exactly the same as shown in Fig. 1 with'the exception of the electrode 16 which instead of being dish shaped has a circular ll-shaped groove cut in it. This enables the current to'travel a much shorter path, after passing through the restricted region 19, and consequently lowers the resistance of the cell considerably. The feature of not interrupting the current flow when the cell is tilted is retained in this modification. Y P I Fig. 3 is a modification ofthe microphone cell of Fig. 1, the difference this time being in the shape of the piston or pusher 15 the shape of the electrode 16 being also slightly di-fl'ererit than that of Fig. 1, in that the dish surface is not so deep but more shallow. The piston-15 whose surface 27 is insulated, has a flange around its edge, extending into the carbon granules and acts on the region 19 opposite the insulated surface of the electrode 16 to exert a varying pressure at thispoint. This arrangement assists in more efie'ctively distributing the granular carbonso the current flowing through the cell will not be interrupted. In addition the moving piston is a great deal lighter so that the strain on the main auxiliary diaphragm will not he so great.

The above describes a preferred embodiment of the invention and it is however to be understood that the same is set forth for illus trative purposes only, and it is not desired to be limited bythe precise construction shown. What is considered new and upon which it is esired to procure Letters Patent is pointed out in the appended claims.

dfhat is claimed is: V 1. In a transmitter, a microphone cell comprising a moving diaphragm and a cup shaped electrode enclosing the cell,'a second electrode attached to the bottom of and insuiated from said cup electrode, granular resistance material in said cell in, contact with said electrodes, an insulated surface on the edge of said second electrode and adjacent to said cup electrode, a current path through said cell comprising said first electrode, said resistance material and a'conducting portion of said second electrode, and means including said moving diaphragm for varying the resistance or said current path.

2. In a transmitter, a microphone cell comprising a cup shaped electrode and a moving diaphragmclosing the opening of the cell, asecond electrode insulated from said cup electrode and attached to the bottom thereof, an insulated rim on the circumference of saidsecond electrode parallel with the inside surface of said cup electrode, an insulated fiat edge surrounding a concave portion of said second electrode opposite said moving diaphragm, granular resistance material in said cell; a current path through said cell from the inner wall of said cup electrode, through said resistance material to the concave portion of said second electrode, and means including said moving diaphragm and efiective transverse to said path for varying the resistance of said path.

3. In a transmitter, a microphone element comprising a moving diaphragm with a piston attached thereto and a cup shaped electrode forming the microphone cell, a second electrode supported in said cell and insulated from said first electrode opposite said piston, carbon granules in said cell in contact with said electrodes, an insulated surface on said second electrode to insulate a portion of the electrode from-the carbon granules and a current path through the microphone extending from said cup electrode through said granules to theuninsulated portion of said secondelectrode in a direction transverse to thejlmes of pressure applied by said movlng diaphragm and piston to the carbon granules.

I 4. In a transmitter, a microphone cell, granular resistance mater al therein, a cup shaped electrode forming the walls of said of which form an electrode, an auxiliary dia phragm having a rigid member attached to the center thereof closing the opening of said cup member, a fixed electrodehaving a concave surface arranged opposite said rigid member and mounted on the bottom of said cup member, granular resistance material in said chamber, means for moving said rigid member to compress said resistance material against a flat insulated surface around the I concave portion of said fixed electrode, and a conducting path for a current'flow through said cell extending through said resistance material from the wall of said cup electrode and at right angles to themovement of said rigid member.

6. In a transmitter, a microphone cell comprising a cup'shaped electrode and a moving diaphragm closing the opening of the cell, a second electrode insulated from said cup electrode and attached to the bottom thereof, an insulated rim on the circumference of said second electrode parallel with the inside surface of sa id cup electrode, an. insulated flat edge surrounding a concave portion of said second electrode opposite said moving diaphragm, granular resistance material in said cell; a current path through said cell from the inner wall'of said cup electrode, through -said resistance material to the concave portion' of said second electrode, said path having a restricted portion formed between said moving diaphragm and the fiat edge of said (second electrode, and means including said J moving diaphragm for varying the resist ance of said granularmaterial by varying the cross section of the restricted portion of the Jcurrent path.

7. In a: transmitter, a microphone cell com prising a cup shaped electrode and a diaphragm having a rigid portion enclosing the opening of the cell, aback electrode attached to the bottom of and insulated from said cup electrode, said back electrode having a conprising a cup shaped member the side walls to the concave portion of said rear electrode cave contact surface surrounded by a flat insulated surface and spaced opposite the rigid portion of said diaphragm, granular resistance material in said cell, and a restricted region between the flat insulated surface of the back electrode and the rigid portion of the diaphragm whereby the granular resistance material is agitated by the rigid portion of the diaphragm, the remaining space around the back electrode and-the concave part serving as a means whereby a reserve supply of granular material is maintained for the said restricted region. 8. In a. transmitter, a mierophonecell comprising a cup shaped electrode anda movable diaphragm, a rigid member having an insulated surface in said cell attached to said diaphragm, a rear electrode having a concave surface and a fiat insulated rim surrounding the concave surface spaced opposite said'rigid member, granular resistance material in said chamber, a current path extending from said cup electrode through said granularmaterial to the concave surface of said rear electrode, and means including said diaphragm for varying the resistance of that portion of said path between said rigid member and the flat insulated rimof said rear electrode.

9. In a transmitter, amicrophone cell, a cup shaped electrode and a moving diaphragm closing the opening thereof, a concave rear electrode fastened on the bottom of and insulated from'said cup electrode, granular resistance material in said cell, a

'current path extending from the inside walls of-said cup electrode through said granular material to ,said rear electrode, means on said rear electrode to restrict said current path to the concave portion of said electrode only,

and means including said moving diaphragm and said last means for varying the resistance of said current path.

10. In a transmitter, a microphone cell comprising a cup shaped member having an inside wall which forms an electrode, a diaphragm attached to the opening of said cup member and having an insulated disk mounted on its center, granular resistance material in said cell, a second electrode mounted on the bottom of said cup member and having a concave surface and a fiat insulated surface surrounding the same, both surfaces spaced opposite said insulated disk, the space formedv between the flat insulated surface and the disk constituting a narrow region where the granular resistance material is agitated at its maximum amount when the diaphragm is vibrated, and a current path through said cell extending from the inner wall electrode of said cup member through said resistance material and across said narrow region to the concave surface of said second electrode, transverse to the movement of said diaphragm and disk at said narrow region.

11. In a'transmitter, a microphone cell, a

cup shaped electrode having an inner Wall forniingan electrode, and an insulated diaphragm closing the opening of said cup, a rear electrode'having a concave exposed sur face and an'insulated flat surface spaced opposite said diaphragm, an insulated rim on said rear electrode parallel with the inner wall of said cup electrode, granular resistance material in said cell, a current path through said cell extending from said inner Wall through said resistance material to said concave surface, means for vibrating said diaphragm to vary the resistance of said material across the space between said diaphragm and said flat insulated surface of said rear electrode, the space between said concave surface and said diaphragm and between the rim of said rear electrode and the inner Wall of said cup electrode comprising regions whereby a reserve supply of granular mate rial is maintained to keep the space between the diaphragm and the flat insulated surface of the rear electrode filled with granular material when said diaphragm is operating.

12. In a transmitter, a microphone cell comprising a cup shaped electrode and a diaphragm for closing the opening thereof, a rear electrode in said cell having a concave surface opposite said diaphragm, granular resistance material in said cell, a conducting path over which current flows through said resistance material extending from said cup electrode to said concave surface of said rear electrode, and means for moving said diaphragm to compress said granular material in a direction transverse to the flow of current over said path.

In witness whereof, I hereunto subscribe my name this 5th day of August, A. D, 1927 ARTHUR BESSEY Sit/5TH. 

